Recently, in the spectacle lens market, demand for lenses which can protect eyes and are friendly to eyes has increased. Many of spectacle lenses have been glass lenses, but, in these days, plastic lenses are mainly used because plastic lenses can protect eyes from accidents which would be caused by broken lenses. Further, materials of plastic lenses have been improved so that the lenses can be hardly broken.
Lenses are required to have a high refractive index and be light and thin, be able to block harmful light to eyes by cutting ultraviolet rays or having a polarizing property, and have stable light-control property such that the color and light transmissivity of lenses can change in response to ambient brightness.
Improvement on thin lenses having high refractive index is being made by casting monomers containing sulfur or the like in molecules. Blocking of harmful light like ultraviolet light is realized by mixing an ultraviolet absorber with optical molding plastic materials. Glaringness to eyes is prevented by mixing an agent, which can absorb light at particular wavelengths, with the optical molding plastic materials, or providing secondary finishing to a lens surface, or providing a lens with a polarizing film.
In order to provide a lens with a color and optical transmissivity variable with ambient brightness, a compound exhibiting a photochromic property is used. Photochromic property or photochromism is the ability of a compound to rapidly change its color reversibly in response to light including ultraviolet rays.
Optical lenses exhibiting high stability and good performance are known as disclosed in JP 08-109039 A and JP 08-234147, which are formed by mixing an inorganic photochromic compound, e.g. Ag-bearing TiO2 or caprous halide, with molten glass.
However, because these lenses are made of glass, they are easy to break and heavy, so that they are less effective in protecting eyes.
Because of the above-described problems with glass lenses, plastic lenses have replaced glass lenses. It was, however, impossible to mix an inorganic photochromic compound with plastic lens materials to produce transparent lenses. Organic photochromic compounds compatible with many of plastic lens materials have been developed recently, and plastic photochromic lenses with good performance have been developed by the use of such organic photochromic compounds. JP 2004-295114 A, JP 2005-514647 A, and JP 2005-199683 A have proposed plastic lenses having their surfaces coated with a coating material with an organic photochromic compound mixed therewith.
Major object of coating the plastic lens with such coating material is to protect the lens base against scratches. The thickness of the coating of most lenses is 5μ or less. This small thickness is caused by difficulty in forming a thick, uniform coating over a curved surface of lens, but such small thickness is sufficient for desired protection of lenses against scratches. In order to provide sufficient photochromism to the coating, it is necessary to add a considerable amount of an organic photochromic compound to the coating material, which may reduce scratch-preventing ability desired for the coating and may reduce adhesion of the coating to the lens base.
JP 61-236521 A discloses a method of producing lenses by casting a typical plastic lens resin material with an organic photochromic compound added to it. A major constituent of most of the resin materials cast shown in this publication low-cost vinyl monomer, and, therefore, the strength of the resulting lenses is too small to protect eyes. They are weak against shock and, therefore, easily broken. In addition, such material requires a large amount of organic photochromic compound to be added, which results in high costs of the resultant products. Recently, lenses made by casting urethane prepolymer which are hard to crack are available, but urethane prepolymer requires a curing time four or five times as long as that of vinyl monomer resins, which means that the productivity of urethane prepolymer lenses is low, and, therefore, the costs of urethane prepolymer lenses are very high.
Recently, many techniques for manufacturing, with improved productivity, optical lenses with organic photochromic compounds used therein, have been developed. For example, JP 2002-196103 A discloses a method of manufacturing a lens-shaped product by forming a laminate sheet including polycarbonate sheets bonded together by means of a urethane adhesive with an organic photochromic compound mixed therein, and thermally bending the laminate sheet into a lens shape. Also, JP 2002-062423 A proposes a laminate sheet including polycarbonate sheets between which a polyurethane resin layer with an organic photochromic compound mixed therein and a polarizing film are interposed.
The laminate sheets disclosed in these publications include an organic photochromic compound containing resin film sandwiched between polycarbonate sheets. The optical surface accuracy of the laminate sheets is not enough, and sunglasses made of the laminate sheets exhibit astigmatism. Therefore, in areas including Australia and Europe, the use of such sunglasses is prohibited.
U.S. Pat. No. 7,036,932 and No. 7,048,997 disclose a method of manufacturing photochromic and polarizing optical lenses by injection molding of optical molding resins. According to the methods disclosed in these U.S. patents, a laminate sheet is formed by preparing a transparent, thermoplastic resin film, which will provide a front surface of a resulting lens, bonding a film of transparent resin with an organic photochromic compound mixed therein to the rear surface of the front transparent, thermoplastic resin film, bonding a polarizing film to the rear surface of the photochromic compound containing film, and bonding a film of thermoplastic resin compatible with a molding resin to the rear surface of the polarizing film. Then, the resulting laminate sheet is subjected to hot bending to form it to have intended contours. The hot-bent laminate sheet is placed in a mold, and the molding resin is injected into the mold to thereby form a photochromic, polarizing optical lens.
The lenses made according to these two U.S. patents are generally satisfactory in optical performance and mechanical strength. However, the thermoplastic films used in these patents are made chiefly of polycarbonate resin, and, accordingly, are less chemically resistant. Therefore, when the lens is used in combination with a plastic frame, a plasticizer in the frame may attack the lens and cause cracks over the entire surface of the lens. Further, since the polarizing film used is formed of a polyvinyl alcohol film dyed with a dichromatic dyestuff to provide the lens with a color in addition to polarizing ability, the lens as a whole exhibits a dark color, and, even the light transmissivity of even a transparent lens is only about 30%. In order to obtain a light transmissivity of about 40%, the polarization degree decreases to 90% or smaller. This means that the lens cannot exhibit polarizing ability. Furthermore, a photochromic compound used with such dark polarizing lens provides the lens with a narrow range of color change, so that the highest performance as a photochromic lens can hardly be exhibited.
WO 01/077723, JP 2005-215640 A, and U.S. Pat. No. 6,814,896 disclose a method of producing a photochromic lens by embedding, in a thermosetting resin, a lens sheet including polycarbonate sheets and a thermosetting polyurethane layer containing a photochromic compound disposed between the polycarbonate sheets. However, the major constituent of the lenses produced by these methods is polycarbonate, and, therefore, the lenses are less chemically resistant. Therefore, when the lens is used in combination with a plastic frame, a plasticizer in the frame may attack the lens and cause cracks over the entire surface of the lens.
In manufacturing a polarizing and photochromic optical lens by injection molding, the important issues are how to control the lens transparency and how to economically provide a variety of colors of the lenses.
According to prior art, the color of a polarizing film is deep in order to provide the film with an increased polarizing property, and, therefore, even if the lens is provided with a photochromic property, significant color tone changes cannot be expected. Furthermore, since the polarizing film must be prepared for each of a large number of different colored lenses, such manufacturing method is not economical. The present invention has been made to solve the above-described technical and economical problems.
A molded laminate having polarizing property is disclosed in Japanese Patent No. 3,681,325 issued to the inventor of the present application. According to the present invention, the laminate disclosed in this Japanese Patent No. 3,681,325 is used as the base. The base used is a laminate molding sheet, which includes a polarizing film having high light transmissivity and high polarization degree for use in liquid crystal displays, first and second cellulose triacetate films bonded to respective ones of the opposing surfaces of the polarizing film, and a resin film bonded to the surface of the first cellulose triacetate film, which resin film is compatible with a lens forming resin. An adhesive with an organic photochromic compound mixed therein is applied over the surface of the second cellulose triacetate film, and, then, a third cellulose triacetate film is disposed over the adhesive to thereby bond the third cellulose triacetate film to the second cellulose triacetate film. The third cellulose triacetate film should be free of ultraviolet light absorber.